hey heres a builders question for you guys

ok heres the deal my 530lb 98gp1200 gets almost 1 hour and 45minutes worth of gas to the tank if im lucky! my cousins 900lb fx140 gets 3.5 hours out of the same gas tank, bigger ski more power same gas tank double the time! is it physically possible to put an fx-140 or 140ho motor in there or any other small decent powered yamaha 4strokes? im going to measure it all out today just seeing if anybody has any suggestions.
dont tell me to get another ski, nobody makes small sitdowns if it was up to me id get a 96xp seadoo and put the rxp motor in it! i do not like big ski's sorry guys my personal preference.
hey so if anybody has a decent 4 stroke ill give you my 60 original hour 1200 motor with 120psi in all 3 cylinders which runs mint!

You've found just what I did, the GP's are a bit of a gas hog compared to the new ones. I had, until last year, a Group K ported sleeper 98 GP1200, and an 01 GPR with mild mods. GP was much faster holeshot, and great for jumping waves, but rough on the ride, GPR faster on top by 3 mph. Riding with a friend on the GP and me on the GPR, we rode together all afternoon, same speeds and stuff, when we filled up afterwords, the GP took 9.6 gallons, the GPR 6.4. I had never realized just how much difference there was, and how much better the new models were, even though faster and heavier. Guess thats progress.

its called efficiency. look at car motors 30 years ago you were lucky to find a 6.0L motor (383) that would get anything above 10 miles per gallon... now you can find the same thing in a new corvette get 20+mpg and run a 12.4 in the 1/4 mile with the air on

so i could even put in a 1200r or 1300r motor and have better gas mileage out of it! does my 1200 motor have the same bottom end as a 1300r? no right? i love the smaller hull. is the gpr motor the same on gas as the fx140/ho motors? dropping a 1300r motor in would be alot easier im guessing and probably wouldnt have to swap all that much out. all in all id like to go out for 3.5hours like my cousins fx140 or my friend rxp!

Get in touch with Group K. They specialized in GP endurance boats for many years. They might have a much simpler option for you. If you could figure out how to get in Touch with Mark Dobson, he also has TONS of info on GP endurance boats.

Have you considered talking to some of the Polaris boyz on the site about the use of Keihen carbs? A 40mm Kehien carb is a very economical carb, that will drastically increase your mileage and range. You "might" burn up a piston or two before you get it perfect, but the cost would be minimal.

A FX has a much larger gas tank than your GP too. It has a 18.5 gallon gas tank. If I remember correctly, that GP has a 13.2 gallon tank. You are running with approximately 2/3'rds his size tank... They aren't the same.

I'd say another option would be to get a bigger tank made. You might be able to squeeze in a 15gallon tank or larger with some bending. I run a 18 gallon tank from a XLT1200 in my GPR. There are aftermarket companies that make "Marine Fuel Cells." We are talking some coin, but it's a feasible option. I'd bet you need to pull the engine to get a larger tank in.

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You might need some fabrication skills or folks that can help you. Heck maybe it will drop right in!

You are on the edge of what will eventually be the norm... folks wanting 2 seaters and nobody making them. Oh sure we have manufacuters making 3seater hulls and putting a small seat on them, but that isn't what you want.

Since YOU are considering it, then guess what? Nobody has probably done it yet. The easiest route is to find a fx140 or 160 with a mucked up hull... shouldn't be too hard. This will be your big investment.

Measure up the engine opening on both. If the gp opening is smaller than the fx, I'd be worried. See if you can get a tape measure from the bottom of the ski to the crankshaft output on both. If the fx crankshaft output centerline is drastically higher, I'd say forgettaboutit.

If you don't have an engine hoist or cherry picker, I'd highly recommend one.

If you get that far, take out your 65U, pipe, and as much as you can from the gp. Hoist the new engine down in there. If the HEIGHT of the engine-output can be made lower than the HEIGHT of the driveshaft, then you got a fighting chance. Remember, he has a rpm reducer box on the back of that engine, so keep that in mind. After that, it's pretty much up to you to make it right. Consider fabricating all your stuff in mild steel for cost. Have them made in SST or aluminum after it works.

does anybody make or plans on making a smaller 2 seater like the 1200 with a good sized 4stroke engine in it. if your 1300r out of the box is 170hp? and 655lbs cant a 540lb 160hp 4stroke (gp1200 with fx140-ho motor) put out the same numbers? and you can always throw a supercharger kit on the fx140-ho motor right. so 200hp is easy to get too...... IMO this would be better then a 900lb rxp. it cant be this easy can it i must be missing something

Lets me see,
yamaha has the complete hull
yamaha has the engine
riva has the rpm kit that brings the 900lb fx140 from 59 to 64 what could that mean with 350lbs off of it...... I say 70mph
AND THEN A SUPERCHARGER on top of this what the hell is the problem, ok who i do i email this too. im not as knowledged as most of you guys but come on this sounds to me like an 85mph ski out of the box if done like this.
Ok now all yamaha would have to do is fix the stupid "porposing" of the hull trim tabs built into it?
Im going to make one of these i know there would have to be a market for this, you gpr guys cant even disagree with this. somebody please tell me why this isnt done already i have to be missing something here! this is way to easy. my god every ski out there is 19ft long seats 14people and weight more then a freakin volkswagon!

i posted in the classifieds for a hull, im going to try to do this. but i need to know the exact dimensions the the fx140-ho motor to make sure this is doable does yamaha plan on having any other 4 stroke motors. maybe ill drop my r6 motor in there similiar enough arent they lol. wait no serioussly i think this might be real cool lol put it in 6th gear and just leave it. 15,000rpm thats it im going to go over 100mph now.

disregard my motorcycle motor plan i already found out why that cant be used